1. Field of the Invention
This invention relates to a magnetic disk cartridge which is used as a recording medium for computers, video devices, or the like. This invention particularly relates to an improvement in the material constituting a cartridge body of a magnetic disk cartridge.
2. Description of the Prior Art
Recently, magnetic disk cartridges are utilized as recording media for computers, video devices, or the like.
In general, a magnetic disk cartridge is provided with a cartridge body, which is constituted of an upper shell half and a lower shell half. A circular opening is formed at the center part of each of the upper and lower surfaces of the cartridge body. A magnetic disk is housed in the cartridge body such that a center core of the magnetic disk may face the circular openings formed at the center parts of the upper and lower surfaces of the cartridge body. Also an opening, into which a magnetic head of a signal recording unit is to be inserted, is formed at least in the upper surface or the lower surface of the cartridge body. Normally, the opening, into which a magnetic head of a signal recording unit is to be inserted, is closed by a shutter. The shutter is constituted of a metal, such as stainless steel. When a signal is to be recorded on the magnetic disk, the magnetic disk cartridge is fed into a signal recording unit. At this time, the shutter slides over the surface of the cartridge body. In this manner, the shutter moves away from the opening, into which the magnetic head of the signal recording unit is to be inserted. Thereafter, the magnetic head of the signal recording unit passes through the opening and comes into contact with the magnetic disk. When the recording of a signal is completed and the magnetic disk cartridge is discharged from the signal recording unit, the shutter slides over the surface of the cartridge body to the opening and closes the opening.
As described above, the shutter constituted of a metal slides over the surface of the cartridge body at the position of the opening, into which the magnetic head of the signal recording unit is to be inserted. Therefore, the cartridge body is easily abraded by the shutter, and some fragmentation of the cartridge body occur. The minute fragments of the cartridge body fall to the magnetic disk and cause drop-outs to occur. In order for such problems to be eliminated, ABS resins having good abrasion resistance have heretofore been employed as the materials constituting the cartridge bodies.
ABS resins have good abrasion resistance. However, the ABS resins are expensive. Therefore, in cases where an ABS resin is employed as the material constituting the cartridge body, the manufacturing cost of the magnetic disk cartridge cannot be kept low.
It may be considered that high-impact polystyrene, which is inexpensive, be employed as an alternative to the ABS resin. However, the abrasion resistance of high-impact polystyrene is poor. Therefore, in cases where high-impact polystyrene is employed as the material constituting the cartridge body, there is the risk that the drop-out occurrence rate cannot be kept low.
Also, from a commercial viewpoint, the magnetic disk cartridge should have a good appearance. Therefore, it is desirable that the cartridge body has a glossy finish.